The Primate Page

Distribution & Habitat

Mountain Gorillas are only found in Central Africa, within the montane rainforests of the Virgunga Volcanoes. Most roam the slopes of three of the dormant volcanoes: Karisimbi, Mikeno, and Visoke ("Mountain Gorillas" 2003). This area is divided by three countries and includes portions of three national parks: Mgahinga Gorilla in south-west Uganda; Volcanoes, in north-west Rwanda; and Virunga, in the eastern Democratic Republic of Congo (DRC). The Virungas are part of the Albertine Rift Valley. This ecoregion is one of Africa’s most diverse, and the Moutain Gorilla is one of its many endemic plant and animal species.

Montane rainforests are also known as cloud forests; they are often cloudy, misty and cool. Those inhabited by the Mountain Gorillas range in altitude from 2225 to 4267 meters (7300-14000 ft). The dense vegetation growing at the lower elevations becomes increasingly less so toward the peaks, where temperatures may drop bellow freezing. George Schaller (1963) identified ten distinct vegetation zones, including: bamboo (Arundinaria alpina) forest at 2225–2804 m (7300–9200 ft); Hagenia (Hagenia abyssinica) forest at 2804–3353 m (9200–1100 ft); and the giant senecio (Senecio erici-rosenii) zone at 3444–4267 m (11300–14000 ft). Hagenia, bamboo, and mixed Hagenia-bamboo forests cover the majority of the volcanoes, along with smaller sections of grassy meadows, subalpine and alpine zones.

Range & Diet

Mountain Gorillas usually include several different vegetation zones within their home range. They spend most of their time in the Hagenia forests, travel to the bamboo forests during the few months of the year fresh shoots are available, and climb into the subalpine regions to eat the soft centers of giant senecio trees ("Mountain Gorillas" 2003). The amount a group travels depends on the availability of these food sources. The average annual home range covers about 8 km² (Watts 1998, 2000). The average day range is 500 m (Fleagle 1988). Mountain Gorillas are extremely destructive when feeding, often consuming many or all parts of each plant. Their ranging patterns include regularly harvesting and destroying patches of rapidly regenerating vegetation (Fleagle 1988).

Mountain Gorillas have the most folivorous diet of any living ape (Fleagle, 1988). The majority of their diet is composed of the leaves, stems, and pith (85.8%) of 62 plant species, mainly Galium vines, thistles, celery and nettles (Watts 1996). Galium vines are found year-round in the Hagenia forests. All parts of this vine are consumed: leaves, stems, flowers, and berries ("Mountain Gorillas" 2003). Bamboo is available seasonally, and it is the primary food source for a few months each year. Mountain Gorillas also feed on bark (6.9%), roots (3.3%), flowers (2.3%), and fruit (1.7%), as well as larvae, snails and ants (0.1%) (Rowe 1996). Dirt and feces are also consumed occasionally, probably for specific minerals and nutrients that can not be obtained from plants (Estes, 1991). Adult males can eat up to 75 pounds of vegetation a day, while a female can eat as much as 40 pounds.

Activity Patterns

Mountain gorillas are diurnal, and they are most active between 6:00 a.m. and 6:00 p.m. Nearly half of these hours are spent eating, as large quantities of food are needed to sustain their massive bulk. Mountain Gorillas do not have to travel as far as other gorillas do in search of food; most of the remaining hours are spent resting. In an average day, they forage in the early morning, rest during the late morning, and they forage again in the afternoon before resting at night.

Mountain Gorillas usually sleep on the ground. Each gorilla builds a nest from surrounding vegetation to sleep in, constructing a new one every evening. Only infants sleep in the same nest as their mothers. Night nests are built by layering plants and thin branches to create a springy platform. The gorillas leave their sleeping sites when the sun rises at around 6 am, except when it is cold and overcast; then they often stay longer in their nests (Schaller, 1963).